Tanning formulations

ABSTRACT

Tanning formulations containing a reaction product of a dialdehyde, which may be totally acetalized, with formaldehyde.

United States Patent Erdmann et a1.

[451 Sept. 30, 1975 TANNING FORMULATIONS Inventors: Hans Erdmann, Heidelberg; Franz Friedrich Miller, Ludwigshafen, both of Germany Assignee: Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed: Mar. 28, 1973 Appl. No: 345,506

Foreign Application Priority Data Apr. 1, 1972 Germany 2215948 June 7, 1972 Germany 2227598 Sept 7, 1972 Germany 2243826 U.S. CI 8/9433; 8/9426 Int. GL C14C 3/16 Field of Search 8/9433, 94.26

Primary Examiner-Ralph S. Kendall Assistant E.\'aminerDennis L. Albrecht Attorney, Agent, or F irm-J0hnston, Keil, Thompson & Shurtleff [57] ABSTRACT Tanning formulations containing a reaction product of a dialdehyde, which may be totally acetalized, with formaldehyde.

3 Claims, N0 Drawings TANNING FORMULATIONS This invention relates to novel tanning formulations based on reaction products of emf-dialdehydes with formaldehyde.

The invention also relates to tanning and retanning with the novel tanning formulations.

A large number of tanning agents and tanning pro cesses have been proposed for use in the tanning industry.

One tanning agent which has been used for many years is formaldehyde. Leathers tanned with formaldehyde are pure white and have a shrink temperature of from 9092C when tanning is carried out at pl-ls of from seven to eight. However, it suffers from the disadvantage that the fullness, softness, flexibility and tensile strength of the resulting leathers are not satisfactory in all respects.

Further research in aldehyde tanning agents has given rise to the use of a ,w'-dialdehydes, in particular glutaraldehyde. Thus US. Pat. No. 2,941,859 teaches that the last-named dialdehyde is a particularlysuitable tanning agent. This patent describes a number of advantages of the leather resulting from tanning with this compound. Particular stress is laid on the distinct improvement in softness and flexibility, the high shrink temperature of about 88C at relatively low pHs (4.0) and the excellent tensile strength. These specific properties have made the dialdehydes somewhat superior to formaldehyde.

This reference also points out that excellent results are achieved when tanning with glutaraldehyde, particularly in combination with mineral tanning agents such as chrome, aluminum and zirconium or with a vegetable tanning agent such as quebracho, sulfited quebracho, or wattle.

However, the drawback of tanning with w,w'-dialdehydes alone is that yellowed leathers are frequently obtained. w,w-dia1dehyde reacts with amines, amino acids, collagen and keratin to form some intensely yellow Schiffs bases. Possibly other side-reactions occur which result in yellowing of the leather. Particularly undesirable effects occur when tanning with w,w'-dialdehydes on furs, since a fur tanned in this manner yellows strongly not only on the flesh side but also on the hair side.

For the above reasons, tanning with, say, glutaraldehyde alone has hitherto been suitable mainly when darker leathers are required or when chromium tanning is carried out simultaneously, where the color of the chromium is applied to the leather and thus masks any yellowing which might occur.

It is an object of the present invention to provide tanning formulations based on w,w'-dialdehydes which do not produce yellowing of the kind mentioned.

A further object is to provide formulations which give approximately the same optimum results as achieved with dialdehydes as regards softness, fullness, tensile strength and shrink resistance.

Yet another object of the invention is to provide formulations of the kind mentioned which give optimum results when used in conjunction with mineral or vegetable tannages.

The objects are achieved with tanning formulations containing at least one reaction product of one molar portion of a C w,m'-dialdehyde, or an amount of a mixture of w,w-dialdehydes of from 2 to 8 carbon atoms equivalent to one molar portion, and from 4 to 6 molar portions of formaldehyde.

The formulations of the invention are simple to produce, conveniently by mixing commercial aqueous solutions of dialdehyde, usually containing from 25 to 50% dialdehyde, with usually 30 to 40% w/w formaldehyde (formal in) solutions and heating the combined solutions to from to 95C and preferably to about C for from 30 to 60 minutes. The reaction proceeds best at pHs near the neutral point, preferably from pH 5 to 7. The pH may be conveniently adjusted with aqueous alkaline solutions such as caustic soda, caustic potash or sodium carbonate solution. A preferred method permits a pH of about 6.5.

A particularly favorable tanning formulation is produced when the reaction is carried out in the presence of from 5 to 20% by weight, based on w,w'-dialdehydes used, of at least one tertiary alkanolamine having from 2 to 4 carbon atoms per alkanol group.

Similarly preferred tanning agents are produced when the w,w-dialdehydes used in the reaction of the invention are not the simple w,w-dialdehydes but complete acetals thereof. Particularly suitable acetals are obtained when the alcohols used for the purpose are those having from 1 to 10 carbon atoms. Here again, the preparation may be carried out in the presence of the above tertiary alkanolamines.

When tanning is carried out with such preferred tanning agents, it is possible to achieve excellent results on leathers, the tanning of which takes a long time, without there being any risk of a weakening in the tanning action and thus of incomplete penetration. Thus the two last-named modifications are mainly suitable for work on furs.

In the manufacture of the tanning agents, the temperatures may be maintained at the required values by cooling of the reaction mixture in known manner. It is particularly important to maintain the above molar ratio of m,w"dialdehyde or dialdehyde mixture or appropriate acetal to formaldehyde at from 1:4 to 1:6 in order to achieve the object of the invention, since at higher formaldehyde contents the tanning properties characteristic of dialdehydes progressively disappear, whilst at lower formaldehyde contents it is no longer possible to eliminate yellowing completely;

Suitable w,w'-dialdehydes for use in the invention are generally all w,m'-dialdehydes or mixtures thereof provided the dialdehydes contain from 2 to 8 carbon atoms and saturated aliphatic CC bonds where they are aldehydes of more than 3 carbon atoms. Examples of suitable representatives are glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, adipaldehyde, pimelaldehyde and sebacaldehyde. Industrially preferred representatives are succinaldehyde, glutaraldehyde, adipaldehyde and glyoxal, of which glutaraldehyde and glyoxal are the most important.

When the acetals of the dialdehydes are used, of which the alcohol components may be alcohols of from 1 to 10 carbon atoms, preferred alcohols for this purpose are methanol, ethanol and propanol, of which methanol is the preferred compound. In this case, care must be taken to ensure that acetalation proceeds to completion. When the formulations are prepared using such acetals, the results are much better, since it has been found that the stability of the formulations may be considerably improved by the use of said acetals.

When tanning is carried out in the presence of alkanolamines, the pl-ls selected are conveniently between 6.5 and 10 and preferably they are maintained at from Preferred alkanolamines for use in the present invention are, in particular, triethanolamine, tri-npropanolamine, tri-isopropanolamine and tri-nbutanolamine.

The fact that the alkanolamines are alkaline-reacting substances means that the pHs which are favorable for 1 our process are not just near the neutral point or in the region of slight acidity, as generally required by the invention, but are in the above-mentioned pH ranges,

particularly in the range pH 7.5 to pH 8.5. Where used, the alkanolamines are added to the reaction mixture conveniently in percentages of from to 20% w/w, based on the w,w'-dialdehyde or corresponding acetal used, preferably in amounts of from 8 to 12%.

The tanning formulations of the invention may be used alone and constitute excellent tanning agents, pretanning agents and post-tanning agents for hide and skins (also referred to below as pelts) or for finished leathers,

Tanning with our novel formulations may be simply carried out, for example, by weakly pickling the pelt material for approx. one hour with 0.6% of formic acid, 5% of common salt and 80% of water, these percentages being based on the weight of the pelt material,

' whereupon from 2 to 20% and preferably about of formulation of the invention is added at pHs of from 4 to 7 and, after a tanning period of about 1 hour, neutralizing with, say, an approx. 1.5% solution of sodium bicarbonate to a pH of from 6 to 7 and continuing for a further 2 hours.

When tanning is carried out with formulations of the invention based on completely acetalized dialdehydes, it is advantageous to add reducing agents such as sodium dithionite or sodium bisulfite to the tanning liquors toward the end of tanning in order to destroy any excess tanning agent. This measure is convenient but notessential when the preparation of the tanning formulations has been carried out in the presence of the aforementioned alkanolamines.

When working on furs, it may be advantageous to use a total tanning period of three hours and to adjust the pickled fur material in the liquor to a pH of from 6 to 7 or, in the case of formulations prepared in the presence of alkanolamines, to from 6 to 8, from the outset and then to add the reaction product of dialdehyde with formaldehyde.

.In the case of pretanning and post-tanning operations, the same amounts of formulation of the invention are used for the pelts and tanned leathers respectively.

Tanning with the formulations of the invention and in particular with the formulations prepared in the preferred manner provides leathers and furs of excellent whiteness and fully equal to leathers tanned with glutaraldehyde alone as regards their other properties such as softness of handle, shrinkage temperature and tensile strength. These findings could not have been expected as one would have assumed that, formaldehyde being present in these products in relatively large excess, the drawbacks of this product would have a decisive influence on the tanning results obtained.

It is particularly surprising that this type of tanning may be carried out with formulations which have been prepared in the presence or tertiary alkanolamines.

One would have expected that the aldehydes would lose their tanning power, since experience shows that masking of an aldehyde grouping by another reactive substance attenuates the action thereof.

Particularly advantageous are combinations with mineral and/or vegetable and/or synthetic tannages. Thus it is possible, for example, to blend the reaction products of the invention with, say, chrome and/or aluminum and/or zirconium tanning agent solutions in any proportions. Blending is conveniently effected so that the chromium, aluminum or zirconium tanning salt is added in such a quantity that 2 moles of metal ions is present per liter of combined formulation. Other mineral tanning agents, synthetic tanning agents and/or vegetable tanning agents which may be used and their optimum proportions are known in the art and therefore require no further explanation in this specification. In the last-named method of combining with mineral, vegetable or synthetic tanning agents, the formulations of the invention may be used to particular advantage in pretanning operations but above all in post-tanning processes and also together with the tanning agents used in the main tanning operation, in which latter case the conditions of working are adjusted to meet the demands of the main tanning component. It is convenient to use the same concentrations of formulation of the invention when used in combination with other tanning agents in tanning operations, pretanning operations and post-tanning processes, based on the weight of the pelt or fur being tanned.

The results achieved with our novel formulations both when used alone and when combined with conventional tanning agents of the kinds mentioned are surprising, since it could not have been expected that the reaction of a dialdehyde with formaldehyde would provide tanning agents which operate without producing yellowing effects. On the contrary, one would have expected that the result would be a hydroxyaldehyde (similar to the mechanism of an aldol condensation) which hydroxyaldehyde would be converted under the conditions of the reaction and with the elimination of water to an unsaturated aldehyde, i.e. compounds which are known to be strongly colored. We have not yet been able to discover the actual reactions which take place under the conditions laid down by the invention. Strong evidence for the fact that a definite number and definite types of reaction must take place is the fact that the reactants must be mixed in specific molar proportions, as otherwise the above drawbacks of both formaldehyde tanning and dialdehyde tanning reappear.

The invention is illustrated but not limited by the following Examples, in which the parts are by weight.

. EXAMPLE 1 250 parts of 50% glutaraldehyde are mixed with 750 parts of 30% formaldehyde and the mixture is adjusted to pH 6.5 with soda solution and heated to 90C with reflux cooling. An exothermic reaction commences. The heat of reaction is removed by cooling so that the solution does not exceed 90C. The temperature is maintained at 90C for 30 minutes, whereupon the sothe product are then added and the-liquor isagitated for 3 hours, parts of a fat-liquor for furs being'added in the final hour. The fur ispure white and its shrinkage temperature is 88C. The skins .are then finished off in the usual manner. A

400 parts ofglutaraldehyde are mixed with 600 parts of formaldehyde and the mixture is adjusted to pH 6.5 with soda solution and. allowed to stand for 24 hours. The mixture is then heated to 90C and maintained at this temperature for 1 hour by applying external cooling or heating as necessary. The solution is then cooled.

The finished solution is used for tanning calfskin as follows:

100 parts of calfskin is pickled with a solution of 80 parts of water, 0.6 part of formic acid and 5 parts of sodium chloride. After 1 hour, 15 parts of the product is added to this solution, which is drummed for 1 hour, the liquor then being adjusted to pH 6.5 to 7.0 by the addition of 1.5 parts of sodium bicarbonate, whereupon the reaction is allowed to continue for a further 2 hours. The leather is white and has a shrinkage temperature of 86C. The leather is then rinsed, fatliquored and finished off as usual.

EXAMPLE 3 145 parts of 40% glyoxal are mixed with 400 parts of 30% formaldehyde and the mixture is adjusted to pH 6.5 with soda solution and then heated to 90C under reflux. A weak exothermic reaction begins. The mixture is held at 90C for 1 hour and then cooled.

The finished solution may be used for tanning as described in Examples 1 and 2.

EXAMPLE 4 The tanning formulation described in Example 1 is mixed with a solution containing 600 parts of a 33% basic chromium(lll) sulfate (equivalent to 2 moles of chromium) in 1 liter, mixing being effected at a ratio by volume of 1:1. The resulting solution is used for tanning, in which pickling, tanning and neutralizing of the pelt material is carried out as for conventional chrome tanning.

EXAMPLE 5 The tanning formulation described in Example 2 is mixed with a solution containing 452 parts of a 66% basic aluminum chloride (equivalent to 2 moles of aluminum) in 1 liter, mixing being effected in a ratio by volume of 2:1. This solution is used for tanning, the pickling, tanning and neutralizing of the pelt material being carried out as for conventional aluminum tanning.

EXAMPLE 6 a"6 outas forconventional self-neutralizing. chrome tanning.

YEXAMPLW @200, parts of 50% glut araldehyde are mixed with 130 parts of methanol and the mixture is adjusted to pH 1.0

to 11.5 with, for example; 2.4 parts by'weight or 2.0

T The mixture is: heated .to 60C forl hour.

This mixture isthen neutralized by adding 1.6 parts by weight of sodaor 7.6 parts by volume of a 2M soda solution, whereupon 400 parts of 30% formaldehyde are added and the pH of the mixture is readjusted to from 6 to 7 and preferably to 6.5 by this addition of acid or soda as required. This mixture is heated at C for 30 minutes and then cooled to 25C.

a. 100 parts of washed, bleached and pickled lambskin are placed in 2,000 parts of pickling liquor and adjusted to a pH of 4-5 with soda. 30 parts of the product are then added and the skins are agitated for from 5 to 6 hours, from 10 to 20 parts of a fat-liquor for furs I being added during the last two hours. The skins are then spun-dried and then, if necessary, agitated for 15 minutes in a solution containing from 2 to 8 parts of sodium bisulfite or sodium dithionite per liter in order to remove any excess tanning composition, after which they are again spun-dried and dried out.

The fur is pure white and-the leather is very soft and shows good handle. The shrinkage temperature is 80C.

b. 100 parts of calfskin is treated in a pickling bath consisting of 0.6 part of formic acid, 5 parts of sodium chloride and 80 parts of water, for 1 hour. There are then added 20 parts of the tanning composition to said pickling bath, which is agitated for 2 hours. There are then added 2 parts of sodium dithionite followed by agitation for 15 minutes. To the bath there are then added 50 parts of an 83.3% basic aluminum chloride solution (containing 2 moles of aluminum per liter) and 0.2 part of chromium formate. After a tanning period of from .3 to 4 hours, the bath is neutralized to pH 5.5 to 5.8

with sodium bicarbonate and tanning is continued for a further 2 hours. The leathers are then horsed up overnight. The skins are then rinsed, fat-liquored and tinished off as usual. The resulting leathers are pure white, very soft and shows good handle. The shrinkage temperature is C.

EXAMPLE 8 200 parts of 50% glutardialdehyde are mixed with 400 parts of 30% formaldehyde and the mixture is adjusted to pH 8.0 by the addition of triethanolamine, for which purpose about 10 parts of amine are necessary. The mixture is heated at 90C for 2 hours and then cooled.

parts of washed, bleached and pickled lambskin are placed in 1,000 parts of a pickling bath and adjusted to a pH of from 7 to 7.5 with sodium bicarbonate. When a constant pH has been established, from 10 to 15 parts of the product are'added and the bath is agitated for 4 hours. There are then added from 8 to 10 parts of a fat-liquor for furs, and the furs are held in the bath overnight. The furs are then spin-dried and tinished off as usual.

The fur is pure white and the leather is very soft and shows good handle. The shrinkage temperature is 85C.

We claim:

aqueous solution, for from 30 to 120 minutes at 80 to 95C and at a pH of from 6.5 to 10 in the presence of from 5 to 20% by weight, based on said dialdehyde of at least one trialkanol amine having from 2 to 4 carbon atoms in each alkanol group.

2. A tanning composition as claimed in claim 1 wherein reactant (A) is glutaraldehyde or glyoxal.

3. A tanning composition as claimed in claim 1 wherein reactant (A) is the complete acetal of glutaraldehyde or glyoxal in which the alcohol component of said acetal is selected from the group consisting of methanol, ethanol and propanol. 

1. A TANING COMPOSITION COMPRISING A REACTION PRODUCT OBTAINED BY THE PROCESS OF REACTING 1 MOLAR PORTION OF (A) A C2-8W,W''-DIALDEHYDE OR THE COMPLETE ACETAL OF SAID DIALDEHYLE OF WHICH THE ALCOHOL COMPONENT CONTAINS FROM 1 TO 10 CARBON ATOMS, OR AN AMOUNT OF A MIXTURE OF SAID C2-8W,W''-DIALDEHYDES OR SAID ACETALS EQUIVALENT TO 1 MOLAR PORTION IN THE FORM OF A 25 TO 50% W/W AQUEOUS SOLUTION, WITH (B) 4 TO 6 MOLAR PORTIONS OF FORMALDEHYDE, IN THE FORM OF A 30 TO 40% W/W AQUEOUS SOLUTION FOR, FROM 30 TO 120 MINUTES AT 80* TO 95*C AND AT A PH OF FRROM 6.5 TO 10 IN THE PRESENCE OF FROM 5 TO 20% BY WEIGHT BASED ON SAID DIALDEHYDE OF AT LEAST ONE TRIALKANOL AMINE HAVING FROM 2 TO 4 CARBON ATOMS IN EACH ALKANOL GROUP.
 2. A tanning composition as claimed in claim 1 wherein reactant (A) is glutaraldehyde or glyoxal.
 3. A tanning composition as claimed in claim 1 wherein reactant (A) is the complete acetal of glutaraldehyde or glyoxal in which the alcohol component of said acetal is selected from the group consisting of methanol, ethanol and propanol. 